This invention relates to Faraday shields, particularly to Faraday shields used in conjunction with a transformer and most particularly to Faraday shields used in conjunction with a planar transformer.
Faraday shields have been placed between the primary and secondary windings of a transformer to reduce the electromagnetic interference or noise capacitively coupled between the windings of the transformer. The noise is often created by dv/dt signals cause by, for example, field effect transistor (FET) drain voltages or diode snaps. Transformers have included Faraday shields between the windings to reduce the noise coupled between the windings.
A typical prior art Faraday shield is a continuous solid layer of copper connected to a voltage source so as to guard against noise being coupled between the windings. The Faraday shield reduces the capacitively coupled noise by reducing the interwinding capacitance of the transformer. However, addition of the Faraday shield adds resistive losses to the transformer. The resistive losses or I2R losses result from eddy currents being induced in the Faraday shield. Until such time as a superconductor can replace the conductive materials used to make the Faraday shield, it will be impossible to eliminate resistive losses due to eddy currents.
In view of the foregoing short comings associated with previous Faraday shields, there is a strong need in the art for an improved Faraday shield having low eddy current losses while maintaining a low noise environment for the transformer.
The present invention includes a Faraday shield having low conductivity areas that reduce resistive losses associated with eddy currents while the high conductive areas of the Faraday shield guard against the occurrence of noise in a transformer. The Faraday shield of the present invention, like the Faraday shields of the prior art, reduces electromagnetic interference or noise in the transformer. Noise typically results from dv/dt signals generated by FET drain voltages and diode snaps, although noise from other sources also occurs, and is coupled between the windings by the interwinding capacitance. Faraday shields, when placed between the windings, guard against the coupling of noise between the windings. The reduction of noise results in a more ideal transformer.
However, the transformer flux is not ideally oriented and thus induces eddy currents which flow in loops in the Faraday shield. Resistive losses occur as a result of the flux because the conductive material which forms the Faraday shields is not a perfect conductor. The resistive losses make the transformer a less ideal transformer. To avoid this problem the present invention includes low conductivity areas in the Faraday shield. The low conductivity areas in the Faraday shield inhibit the looping eddy currents thereby reducing the resistive losses. Accordingly, a more ideal transformer is achieved through the use of the Faraday shield of the present invention.
To accomplish the foregoing and related ends, the invention comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.
The present invention will now be described more fully with reference to the accompanying drawings in which several embodiments of the invention are shown. The present invention, however, may be embodied in many different forms and should not be construed as limited to the embodiment shown. The several embodiments described are provided.